Blue smoke on start up

[Gaz 1042]

I have started to notice a puff of blue smoke on start up after the car has been sitting for awhile.

Some quick research turns up valve seals regularly. Sound about right? Any other opinions? And is it a big job to do?

Cheers.

[hybrid 1039]

Take your air box off/apart and have a look at the MAF. If its oily you're probably just suffering from 'blow by'

It happens when you have a pressure build up in the crank case and vents into the intake system via a tube. EG too much oil (over filling oil) or other things like oil thermostats stuck closed (generally only on M cars) or racing your car around the track (running high revs all the time). An oil mist will build up over time over the inside of the intake system.

If you get a build up of oil after it rests for period of time in the throttle body (part of the intake system), when you open the throttle up it will burn off the oil in a puff of blue smoke. If it only happens for a small amount of time on start up, it just excess blow by burn off. Its not bad, but it also doesnt do your plugs or sensors any favours over a long period of time.

Its the OEM engines way of dealing with excess oil. Another way is an oil catch can, which needs to be plumped correctly to work properly.

Even my old 330i did it after a track session.

Valves symptoms are when you get blue smoke all the time especailly when staying off the throttle down a slope for say 5-10 seconds and pressing the accelerator and you get blue smoke puff out of the back.